The present invention relates generally to improved medical device and methods for using same. More particularly, the present invention relates to a vascular graft implant comprising vascular endothelial growth factor (VEGF) and/or platelet derived growth factor (PDGF) for enhanced site-specific angiogenesis and methods thereof.
The basic function of an arterial blood vessel is for transportation of blood from the heart to organs and tissues of the body. When a blood vessel is diseased or becomes dysfunctional, a vascular graft is usually employed for implantation to replace or assist the diseased or dysfunctional blood vessel. The vascular grafts include autologous blood vessel, homograft, cryo-preserved blood vessel, grafts made of synthetic material such as expanded polytetrafluoroethylene (e-PTFE) or polyester (trade name Dacron), and grafts made of biological material, such as bovine internal mammal artery, human umbilical vein, or pericardium.
A special sub-group that has dysfunctional blood vessels belongs to diabetic patients. Diabetes mellitus is characterized by a broad array of physiologic and anatomic abnormalities, for example, altered glucose disposition, hypertension, retinopathy, abnormal platelet activity, aberrations involving medium and small sized vessels, and other problems. Diabetics may depend on insulin for the prevention of ketoacidosis. Developed atrophic ulcer and infected alterations of the foot as a result of complications of diabetes mellitus may require foot amputation. The current treatment may include drug therapy, for example, U.S. Pat. No. 5,871,769 to Fleming et al. discloses methods for the prevention and/or treatment of diabetes mellitus using magnesium gluconate. However, a biocompatible vascular graft may be implanted to enhance blood circulation and eventually extremity salvage. A vascular graft having enhanced angiogenesis capability or having angiogenesis factors may promote peripheral revascularization or neovascularization for blood perfusion so as to save the diseased foot from amputation. The process of angiogenesis (new capillary formation) is stimulated by angiogenesis factors.
The vascular graft or prosthesis made of synthetic materials is usually porous, compliant, strong, and biocompatible. The micropores of a synthetic prosthesis are believed to facilitate tissue/cells ingrowth from the host so as to accelerate the healing process. It is also suggested that the host cells tend to encapsulate a foreign substrate if the host tissue does not achieve cell infiltration into the substrate. In clinical practices, partially clotted blood, collagen, gelatin or other gelatinous material may be coated upon/into the micropores so that blood leakage during the initial phase of implantation is minimized. U.S. Pat. No. 5,851,230 discloses a vascular graft with a collagen sealant, and the patent is incorporated herein by reference.
The vascular prosthesis made of biological material contains collagen as its major component. A biological prosthesis is usually crosslinked to reduce the antigenicity, enhance its antithrombogenicity, and/or improve the durability. Typical crosslinking agents include glutaraldehyde, formalin, dialdehyde starch, polyepoxy compounds or the like. U.S. Pat. No. 4,082,507 discloses a treatment method with glutaraldehyde, dialdehyde starch and formalin. U.S. Pat. No. 4,806,595 discloses a treatment method with polyepoxy compounds and/or heparin. The implantation with a polyepoxy compounds treated graft usually exhibit much tissue regeneration and capillary proliferation, and may account for some degree of angiogenesis. Both patents are incorporated herein by reference.
When a vascular graft is placed in a human body, the inner walls of the graft may become lined with endothelial cells, which possess antithrombotic properties for preventing blood clotting and deposition of blood thrombus on the inner walls. In actual clinical situations, however, lining by the endothelial cells is usually extremely delayed, and in most cases, only the area of the anastomosis of the vascular graft becomes covered with endothelial cells while remote locations away from the anastomoses are not covered. Accordingly, thrombus continues to deposit on the inner walls where endothelialization is void. Though endothelial seeding or sodding method has been recently developed to assist the endothelialization process, the seeded/sodded cells may separate from the inner wall of a vascular graft and be washed away by the blood stream. For example, U.S. Pat. No. 4,820,626 discloses a method of treating a synthetic or naturally occurring surface with microvascular endothelial cells. One of the major drawbacks is the extra step of collecting autologous endothelial cells, enzymatic digestion by collagenase, centrifugal filtration, and seeding prior to implantation of the graft.
Furthermore, U.S. Pat. No. 5,785,965 discloses a process for sodding modified cells onto a vascular prosthesis for implantation, wherein endothelial cells derived from subcutaneous adipose tissue are genetically modified to express the endothelial cell specific angiogenic factor VEGF. The method accelerates endothelialization on the luminal surface of the vessel. However, during the early stage of transplantation, the sodded cells may separate from the inner wall of a vascular graft and be washed away by the blood stream. It was reported that when endothelial seeding is applied to grafts installed in the canine infrarenal aorta, surface thromboresistance improves significantly over controls only after the seeded grafts have healed for approximately 4 weeks. In the above discussed endothelialization processes, only autologous endothelial cells may be used because of concerns on immunological response. In almost any cell transplantation procedure, immunological response is always a concern.
Noishiki et al. in U.S. Pat. No. 5,387,236 discloses a vascular prosthesis by depositing fragments of biological tissues such as vascular tissues, connective tissues, fat tissues and muscular tissues; and cells such as vascular endothelial cells, smooth muscle cells and fibroblast cells within the wall of a vascular prosthesis. Though the patent discloses a method for effectively depositing cells/tissues into the interstices of a vascular prosthesis, Noishiki et al. does not disclose a method of incorporating vascular endothelial growth factor or platelet derived growth factor to promote angiogenesis and to facilitate in situ proliferation of endothelial cells and/or neovascularization inside the walls of an implanted vascular prosthesis.
The angiogenesis process is believed to begin with the degradation of the basement members by proteases secreted from endothelial cells activated by mitogens such as vascular endothelial growth factor and basic fibroblast growth factor (bFGF). The cells migrate and proliferate, leading to the formation of solid endothelial cell sprouts into the stromal space, then, vascular loops are formed and capillary tubes develop with formation of tight junctions and deposition of new basement membrane. Recent studies have applied vascular endothelial growth factor to expedite and/or augment collateral artery development in animal models of myocardial and hindlimb ischemia. The relationship between growth factors, stem cells and cell progenitors has been documented (Burgess, A and Nicola N., Growth Factors and Stem Cells, Chapter 1, published by Academic Press 1983).
Vascular endothelial growth factor (VEGF) is mitogenic for vascular endothelial cells and consequently is useful in promoting neovascularization (angiogenesis) and reendothelialization. Angiogenesis means the growth of new capillary blood vessels. Angiogenesis is a multi-step process involving capillary endothelial cell proliferation, migration and tissue penetration. VEGF is a growth factor having a cell-specific mitogenic activity. It would be desirable to employ a wound healing substrate incorporating a mitogenic factor having mitogenic activity that is highly specific for vascular endothelial cells following vascular graft surgery, balloon angioplasty or to promote collateral circulation. U.S. Pat. No. 5,194,596 discloses a method for producing VEGF while U.S. Pat. No. 6,040,157 discloses a specific VEGF-2 polypeptide. Both patents are incorporated herein by reference.
U.S. Pat. No. 5,980,887 discloses a method to isolate EC progenitor from circulating blood and methods for enhancing angiogenesis with endothelial progenitor cells in a patient by administering to the patient an effective amount of an isolated endothelial progenitor cell, wherein the endothelial progenitor cell may include CD34+, flk-1xe2x88x92 or tie-1+. However, Isner et al. in U.S. Pat. No. 5,980,887 does not disclose incorporating VEGF onto a medical prosthesis for localized site-specific angiogenesis enhancement.
Hammond et al. in U.S. Pat. No. 5,880,090 discloses methods for enhancing the endothelialization of synthetic vascular grafts by administering to a graft recipient an agent that mobilizes bone marrow derived CD34+ cells into the blood stream, that enhances the adherence to graft surfaces of blood-borne endothelial progenitors. Again, immunological response to any cell transplantation is a clinical concern.
Gordinier et al. in U.S. Pat. No. 5,599,558 discloses a method of making a platelet releasate product and methods of treating tissues with the platelet releasate. Platelet derived growth factor (PDGF) is a well-characterized dimeric glycoprotein with mitogenic and chemoattractant activity for fibroblasts, smooth muscle cells and glial cells. In the presence of PDGF, fibroblasts move into the area of tissue needing repair and are stimulated to divide in the lesion space itself. It has been reported that the cells exposed to lower PDGF concentrations are stimulated to move to environments having higher concentrations of PDGF and divide. The patent is incorporated hereby by reference.
Uncontrolled over-angiogenesis or inappropriate angiogenesis is detrimental to a patient. This inappropriate angiogenesis is mostly related to non site-specific process and may result in proliferation of tumors and/or cancers. For example, it is only after many solid tumors are vascularized as a result of angiogenesis that the tumors begin to grow rapidly and metastasize. Because angiogenesis is so critical to these functions, it must be carefully regulated at any specific site or locality in order to maintain health.
A site-specific angiogenesis by incorporating VEGF and/or PDGF onto a medical material, particularly a cardiovascular device, may attract the progenitor cells, endothelial cells or the like from the circulating blood via a vascular graft to deposit onto the device surface and enhance the needed site-specific angiogenesis at the lesion site. Therefore, there is an urgent clinical need for a vascular graft having incorporated VEGF and/or PDGF onto the graft that may provide angiogenesis factors and circulating blood so as to enhance site-specific neovascularization and angiogenesis at the graft and its proximity to treat diabetic foot.
In general, it is an object of the present invention to provide a method for preparing a vascular graft having site-specific angiogenesis factor, preferably by incorporating vascular endothelial growth factor and/or platelet derived growth factor onto the vascular graft. The vascular graft of the present invention may be used to bypass or repair a part of the diseased/dysfunctional blood vessel. It is a further object of the present invention to provide a vascular graft having site-specific angiogenesis factors comprising incorporating at least one vascular endothelial growth factor, or at least one platelet derived growth factor, or other angiogenesis factor, and combination thereof onto the medical device.
In one preferred embodiment, the vascular graft having site-specific angiogenesis factor comprises at least one vascular endothelial growth factor. Vascular endothelial growth factor, which is also known as vascular permeability factor, is a secreted angiogenic mitogen whose target cell specificity appears to be restricted to vascular endothelial cells. The xe2x80x9cangiogenesis factorxe2x80x9d of the present invention refers to any compound, substrate, material, specie, factor, or element that stimulates or promotes angiogenesis activity. The angiogenesis factor may comprise one of the following: vascular endothelial growth factor, platelet derived growth factor, tissue treatment factor, and the like. The xe2x80x9cvascular endothelial growth factorxe2x80x9d in this invention refers broadly to any and all the members of the vascular endothelial growth factor family, which may comprise polynucleotides, polypeptides encoded by such polynucleotides that facilitate angiogenesis, and the like. U.S. Pat. No. 6,040,157 discloses general characteristics and specific properties of vascular endothelial growth factor and is incorporated herein by reference. VEGF has four different forms of 121, 165, 189 and 206 amino acids due to alternative splicing, which are designated as VEGF121, VEGF165, VEGF189, and VEGF206, respectively.
VEGF121 and VEGF165 are soluble that can be incorporated onto the vascular graft of the present invention. In one embodiment, VEGF121 and/or VEGF165 are mixed with a substrate, such as collagen, heparinized collagen, crosslinked collagen, crosslinked heparinized collagen, blood clot, drug, or the like, prior to be incorporated onto the vascular graft. In another embodiment, the method for incorporating the vascular endothelial growth factor comprises a step of impregnating the growth factor onto the vascular graft. In a further preferred embodiment, the step further comprises applying pressure to force impregnating the vascular endothelial growth factor into the vascular graft, preferably from the inner side or the blood-contacting side of the vascular graft.
VEGF189 and VEGF206 are bound to heparin containing proteoglycans in the cell surface. Therefore, a heparinized medical material, such as the one disclosed by Noishiki et al. (U.S. Pat. Nos. 4,806,595 and 5,387,236), has the capability of incorporating the desired vascular endothelial growth factor by binding VEGF189 and/or VEGF206 for site-specific angiogenesis. Both patents are included herein by reference. The vascular endothelial growth factor of the present invention may be selected from the group consisting of VEGF, VEGF 2, bFGF, VEGF121, VEGF165, VEGF189, and VEGF206.
The xe2x80x9cplatelet derived growth factorxe2x80x9d in this invention may cover broadly PDAF (platelet derived angiogenesis factor), PDGF (platelet derived growth factor), TGF-B (transforming growth factor beta), PDEGF (platelet derived epidermal growth factor), PDWHF (platelet derived wound healing formula), and the like. The platelet derived growth factor of the present invention may also comprise any substrate that contains at least one of the above-referred PDAF, PDGF, TGF-B, PDEGF or PDWHF that possess angiogenesis activity, wherein said substrate may comprise blood clot or blood components. U.S. Pat. No. 5,599,558 to Gordinier et al. discloses general properties and constituents of platelet derived growth factor, and the patent is incorporated herein by reference.
The xe2x80x9ctissue treatment factorxe2x80x9d in this invention may refer to any chemical, substrate, material, and solution that may treat a tissue to render the tissue more angiogenic or have more angiogenesis propensity. A tissue treated by a polyepoxy compound or combinations of polyepoxy compounds, as disclosed in U.S. Pat. No. 4,806,595 has angiogenesibility. A vascular graft incorporating tissue treatment factor would render the medical device with enhanced angiogenesis. The entire content of the patent is incorporated herein by reference.
In accordance with the preferred embodiment of the present invention, the vascular graft may be selected from the group consisting of autologous graft, homograft, biological graft, synthetic graft, composite graft or the like. Furthermore, the biological graft or conduit is selected from the group consisting of internal mammary artery, umbilical vein, urethra, pericardium, jagular vein, genetically altered blood vessel, and combinations thereof. The vascular graft may be either heparinized or crosslinked, wherein an agent for crosslinking the vascular graft may be selected from the group consisting of glutaraldehyde, formalin, dialdehyde starch, polyepoxy compounds, and the like. The vascular graft of the present invention comprises site-specific angiogenesis factor adapted for enhancing angiogenesis.
In a still preferred embodiment, a method for treating diabetic foot of a patient comprising implanting a vascular graft for enhancing blood perfusion, wherein said vascular graft comprises site-specific angiogenesis factor. The angiogenesis factor may be selected from the group consisting of VEGF, VEGF 2, bFGF, VEGF121, VEGF165, VEGF189, VEGF206, PDGF, PDAF, TGF-B, PDEGF, PDWHF, polyepoxy compounds, and combination thereof
Furthermore, a process for implanting a vascular graft having site-specific angiogenesis factor comprises (a) preparing an implantation site; (b) positioning the vascular graft at the implantation site; and (c) implanting the vascular graft. After the graft is in place, the endothelial cells and cells progenitors deposit site-specifically on the device for expedited angiogenesis and mitosis. The vascular graft for the implantation process may comprise at least one vascular endothelial growth factor or platelet derived growth factor, wherein the vascular graft may be selected from the group consisting of autologous graft, homograft, biological graft, synthetic graft, and composite graft.